1. Field of the Invention
This invention relates to a camera module, and more specifically to a camera module that can be used in small-sized electronic apparatuses such as digital cameras, camera-equipped cellular phones and the like.
2. Description of the Prior Art
A camera module having a function of displacing a lens unit in a direction of an optical axis of the lens unit is used in relatively small-sized digital cameras, camera-equipped cellular phones and the like. This function is used for providing an autofocus function and/or zoom function, and is achieved by an interaction between a magnetic field generated by an electrical current flowing in a coil and a magnetic field generated by a yoke and magnets provided on the yoke. Recently, camera modules to be mounted in camera-equipped cellular phones are required to further reduce size and shape thereof.
FIG. 4 shows an actuator assembly for providing an auto-focus function used in a conventional camera module. The actuator assembly 100 includes a holder 103 which houses a lens unit (not shown in the drawing), a coil 101 wound around the holder 103, a base 104 formed into a roughly square shape having four corner posts near the four corner thereof, four magnets 102 respectively arranged near the four corner posts of the base 104, and a spring 105 for resiliently supporting the holder 103.
In the actuator assembly 100, by supplying an electrical current to the coil 101 provided on the holder 103, a repellent force is generated by the magnetic fields provided by the four magnets 102 and the coil 101. Further, by utilizing a spring force of the spring 105, the holder 103 can be displaced up and down directions in the figure to carry out the autofocus function.
One example of a camera module having such an actuator assembly 100 is disclosed in a publication of Japanese Utility Model Registration No. 3124292.
In the actuator assembly 100 described above, the four magnets 102 are arranged on the comers corners of the roughly square-shaped base 104. Therefore, when the entire size of the camera is to be reduced, there is a problem in that sufficient magnetic force cannot be secured in each of the magnets 102. This is because if the thickness of each magnet 102 is reduced, the distance between the N pole and the S pole in each magnet is shortened, thus resulting in a reduced magnetic force.
Further, in the actuator assembly 100 described above, the reduced magnetic force due to the reduced size of each magnet is compensated by the provision of the spring 105. However, if the entire size of the camera module is to be further reduced, there arises another problem in that it becomes difficult to secure a space for providing the spring 105.